1. Field of the Invention
The present invention relates to a microminiature electron source having a vacuum chamber for emitting electrons, the vacuum chamber being disposed at the distal end of a flexible coaxial cable. The microminiature electron source in accordance with the present invention is capable of instantly supplying high peak pulsed power to generate electrons. Because of this feature, the microminiature electron source finds extensive use in the field of medical diagnoses and treatment, including treatment of coronary restenosis, intravascular radiotherapy and cancer therapy, the industrial field, including nondestructive inspection and electron beam irradiation, the field of researches, and the field of microwave electron tubes.
2. Description of the Related Art
Currently, it is said that there are more than 500,000 patients requiring radiotherapy and radiation treatment in the world a year. As a radiation source having a diameter of 2 mm or less, a gamma ray source of cesium or iridium, or a needle or a rod filled with a liquid containing radioactive substance is nowadays being used for medical treatment. The conventional radiotherapy places heavy burdens on both patients and the persons involved in medical treatment. The radiation source employing the radioactive substance constantly emits radioactive rays. Hence, during a preparatory step implemented to locate an affected area of a patient body to be irradiated, a non-affected area will be inevitably irradiated before the patient is subjected to actual medical treatment. This means that extremely complicated handling and high risk have been always involved in the medical treatment, thus further burdening doctors. Accordingly, there have been demands for the development of a small electron medical treatment system that provides high medical treatment effect, causes less burdens on patients, and requires lower total cost.
There has been proposed a pulse X-ray generator using a coaxial line, an electrode, and a target for emitting electrons, although it is not intended for medical treatment (Japanese Examined Patent Application Publication No. 60-20865). The X-ray generator having the coaxial cable uses an inert gas, such as helium, charged in the space between a cold cathode and the target that emits X rays. However, a very small quantity of oxygen gas ions or the like, which are impurities, contained in the inert gas severely collide against the cold cathode, adversely affecting the durability of the cold cathode. Furthermore, since it is not designed for medical treatment, it is bulky as a whole, making it impossible to use it as a radiation source for medical treatment by inserting it into blood vessels, lumens of a body, or tubes.
The inventor has proposed a microminiature X-ray generator (Japanese Patent No. 3090910), which has been achieved by further reducing the size of the foregoing pulse X-ray generator and which generates X rays under the application of high-voltage pulses. The microminiature X-ray generator is considerably advantageous in that no high voltage is applied to generate X rays until an X-ray generating unit is set and ready, thus making it possible to avoid unwanted irradiation to non-affected tissues of a patient body or medical personals involve the treatment.
Accordingly, it is an object of the present invention to improve an electron source used with the foregoing microminiature X-ray generator so as to provide a microminiature microwave electron source that features greater ease of operation and finds further expanded application fields.
In order to achieve the above objections, a microminiature microwave electron source excited by a pulsed microwave power through a coaxial cable to emit electrons according to the present invention includes an electrically conductive cylindrical chamber that is connected to an external conductor of the coaxial cable, and has an opening anode in a bottom portion thereof; a central conductor that has one end thereof connected to a central conductor of the coaxial cable, a cathode formed on the other end thereof being supported by the chamber such that the cathode opposes the anode; and connecting means for electrically and mechanically connecting a chamber assembly comprising a resonator constituted by the chamber and the central conductor with the coaxial cable.
In the microminiature microwave electron source according to the present invention, the cathode is an electric field radiating cold cathode.
In the microminiature microwave electron source according to the present invention, the cold cathode is formed using a carbon nanotube.
In the microminiature microwave electron source according to the present invention, the carbon nanotube is disposed at the center of a distal end of the central conductor, and surrounded by a Welnelt electrode.
In the microminiature microwave electron source according to the present invention, the chamber operates as a resonator of (4/xcex) (2n+1) with respect to a microwave.
In the microminiature microwave electron source according to the present invention, the connecting means removably connects the coaxial cable and the chamber by a screw or sliding sleeve fit.
In the microminiature microwave electron source according to the present invention, a flange is provided at a proximal portion of the central conductor in the chamber, and the flange is secured to the chamber through the intermediary of a coupling iris and constitutes an impedance converter for matching a line impedance of the coaxial cable and an impedance of the resonator of the chamber.
In the microminiature microwave electron source according to the present invention, the opening anode of the chamber assembly has a hermetic window that allows an electron beam to pass therethrough so as to directly irradiate a target by the electrons that have passed through the hermetic window.
In the microminiature microwave electron source according to the present invention, the opening anode of the chamber assembly is connected to another vessel having vacuum space.
In the microminiature microwave electron source according to the present invention, the vacuum space of another vessel is connected to the opening anode of the chamber assembly through the intermediary of a beam collimator.
In the microminiature microwave electron source according to the present invention, another vessel having the vacuum space is an electrode vessel of an RF gun, a linear accelerator, a TWT or a klystron.
In the microminiature microwave electron source according to the present invention, the vacuum space of another vessel is an X-ray generating chamber, comprising an X-ray target, which opposes the anode opening, and an X-ray radiation window, thus making the microminiature microwave electron source applicable for radiating X rays.
In the microminiature microwave electron source according to the present invention, the microminiature microwave electron source is a microminiature X-ray source intermittently driven by microwave bursts.